Indian Journal of Science and Technology, Vol 8(28), DOI: 10.17485/ijst/2015/v8i28/71928, October 2015
ISSN (Print) : 0974-6846
ISSN (Online) : 0974-5645
Comparitive Loss Evaluation of Si IGBT Versus Sic
Mosfet (Silicon Carbide) for 3 Phase Spwm Inverter
Trinadh Mathe1 and K. Narsimha Raju2
KL University, Vijaywada, Andhra Pradesh, India; mathe.trinadh@gmail.com
Department of EEE, KL University, Vijaywada, Andhra Pradesh, India; narsimharaju_eee@kluniversity.in
1
2
Abstract
Background/Objectives: Reducing the losses of 3 phase spwm 2 level inverter by replacing the present semi conductor
switches which are si igbt (silicon) with the latest sic mosfet (silicon carbide) switches. Methods/Statistical Analysis:
si igbt (silicon) and sic mosfet (silicon carbide) are modelled in pspice using the data sheet parameters and the modelled
switches are used to simulate the three phase spwm inverter and the losses of the system are compared. Findings: The
three phase spwm inverter simulated at switching frequency ranges of 5khz, 8khz, 10khz, 15khz and it had been observed
that the losses of the 3 phase spwm sic mosfet inverter are 29% less for 5khz switching frequency, 34% less for switching
frequency of 8khz, 37% less for switching frequency of 10khz, 42% less for the switching frequency of 15khz over the 3
phase spwm inverter based on si igbt. Application/Improvements: The sic mosfet can replace the si igbt in 3 phase spwm
inverter system for better efficiency and the pspice simulations showed similar results showing that sic mosfet is efficient
than si igbt based three phase spwm inverter.
Keywords: Insulated Gate bi Polar Transistor (IGBT), Losses, Metal Oxide Semi Conductor Field Effect Transistor (MOSFET), Silicon (Si), Silicon Carbide (SIC), Sine Pulse Width Modulation (SPWM)
1. Introduction
In 19921 UMOSFET was first among sic mosfet
technology that was developed by cree. Later in 1997
Accufet (Accumulation-channel fet) was developed in NC
State University by Dr. Baliga's group using 6h-sic dmos
geometry and it was the first high voltage (350V) planar
vertical sic (Accufet) developed with buried implanted
region for shielding the gate oxide2. Later in 2001 2.4
KV 4h-sic Dimosfet having specific on state resistance
of 42mΩcm2 was demonstrated by cree3. In 20044,5 Dr.
James Coopers group of Purdue University developed
3KV, 5KV Umosfet of 4h-sic having junction termination
extension (jte) and trench oxide protection. In 20046 10kv,
4h-sic was developed by cree.
Large effort is put into sic research and development
in recent years as the critical electric field of 4h-sic is 8.2
times larger than that of si. So there are more advantages
in using sic devices as their electric break down field,
electron saturated drift velocity, thermal conductivity,
* Author for correspondence
irradiation tolerance making sic available for high voltage,
high temperature and frequency and also combining low
power loss8,9.
Considering case of 22kw inverters used to drive
motors they conventionally employ si igbts that operate
at max temperatures of 125ºc. That has to be mounted on
larger heat sink. As they produce more losses on increasing
the switching frequency and has to be cooled using forced
air cooling or water cooling as their performance is
limiting sic has gained more attention.
2. Semiconductor Property
Related Application
Advantages
Sic devices are expected to enable superior performance
compared to si devices. In view of sic's excellent electrical
and physical properties.
Comparitive Loss Evaluation of Si IGBT Versus Sic Mosfet (Silicon Carbide) for 3 Phase Spwm Inverter
Table 1. Semi conductor property based advantages of silicon carbide (sic) material over silicon (si) material
Semiconductor
Properties (SiC/Si)
Melting Point 2X
Band Gap 3X
Breakdown Lield 10X
Thenmal Conductivity 3X
Device Expected
Perfprmance (Sic / Si)
High Temperature
Operation 2x
High breakdown Voltage 10x
High Current density
Low Loss 1/100x
High Speed 10x
Saturation Carrier Velocity 2X
2.1 Heat Sink
Higher melting point and higher band gap of the sic
based device would allow higher temperature operation
enabling the use of smaller heat sink compared to si based
device.
2.2 Device Count
Higher break down field would result in having higher
break down voltage reducing the device count.
2.3 Efficiency
Higher band gap and higher break down field and higher
thermal conductivity are the reasons for sic having lower
losses and higher efficiency.
Equipment
Achieved Performance (>1KV)
Lmpact
Simple heat sinc 2x (300 degree C) 10
*
3x (350 degree C)
Device number 2.5 x(19.5kv) [12]
*
reduction
1x (12.5kv)
Small size High 1/420x (23m ohm cmsqu) [13]
*
efficiency
1/230x (690m ohm cmsqu) [14]
Small size High 10x (28-100 ns) [15]
*
Speed
3 x (47ns) [14]
index is also taken unity the system specification is in
Table 1.
Table 2. System specification of si igbt based 3 phase
inverter.
Dc voltage
Modulation method
Modulation index
Switching frequency
Power factor
Motor peak current
Power rating
586
SPWM
1
5KHZ,1OKHZ,15KHZ
1
38A
22KW
2.4 Speed
Higher thermal conductivity and higher saturation
carrier velocity would result in smaller seize and high
speed operation.
3. System Specification
Two 3 phase spwm inverters are designed basing on si igbt
and sic mosfets. Figure1 shows the circuit for the si igbt
base 2 level 3 phase spwm inverter. Figure 2 shows the
circuit for sic mosfet based 2 level 3 phase spwm inverter.
For si igbt 3 phase inverter six 1200V, 40A single si
igbts are considered. The inverter operated at 3 ranges of
switching frequencies 5khz, 10khz and 15khz. The inverter
is controlled using spwm technique. For easy evaluation
the power factor is taken as unity and the modulation
2
Vol 8 (28) | October 2015 | www.indjst.org
Figure 1. Si igbt based 3 phase inverter with r load.
Indian Journal of Science and Technology
Trinadh Mathe and K. Narsimha Raju
Table 3. System specification of si igbt based 3 phase
inverter
Dc voltage
Modulation method
Modulation index
Switching frequency
Power factor
Motor peak current
Power rating
Figure 4 shows the forward characteristics of the sic
mosfet used for the evaluation.
586
SPWM
1
5KHZ,1OKHZ,15KHZ
1
38A
22KW
Figure 4. Sic mosfet device characteristics data sheet.
5. Loss Calculation
Figure 2. Sic mosfet based 3 phase inverter with r load.
4. Device Paramaters
The Figures were taken from the data sheets of respective
si igbt and sic mosfet.
Figure 3 shows the forward characteristics of the si igbt
used for the evaluation
The conversion losses in the inverter can be divided in
two categories.
• Conduction loss
• Switching loss
Table 4. Parameter comparison of si igbt vs sic mosfet
considering the same freewheeling diode for both si igbt
and sic mosfet
Rating
Vfo
rf
Eon
Eoff
SI IGBT
SIC MOSFET
3.5V
0.127Ω
3.1mJ
2.4mJ
4.1V
0.166Ω
218µJ
64 µJ
Table 5. Parameter comparison freewheeling diode of si
igbt vs sic mosfet
Vd
Rd
Si IGBT
freewheeling
diode
2.3
0.0836Ω
Sic mosfet
freewheeling
diode
2.3
0.0836Ω
Figure 3. Si igbt device characteristics data sheet.
Vol 8 (28) | October 2015 | www.indjst.org
Indian Journal of Science and Technology
3
Comparitive Loss Evaluation of Si IGBT Versus Sic Mosfet (Silicon Carbide) for 3 Phase Spwm Inverter
5.1 Conduction Losses
The conduction losses are due to device on-state voltage
drop. They calculated by averaging the conduction losses
in each switching cycle as shown in below equation:
1 T
Pc = ∫ V f (wt )i(wt )dwt (1)
T 0
Where PC is the total device conduction losses,
switching period is T. Vf (wt) is the forward voltage of the
device, i (wt) is the current flow through the device in the
conduction period. The value of Vf (wt) is calculated as
follow:
V f = V fo + rf i(t ) (2)
Where Vf0 is the device forward voltage at no load and
device forward resistance is rf. The values of Vf0 and rf are
calculated using the datasheet of device characteristics
provided by manufacturing companies as shown in Figure
3, 4. The rf is the ratio between the collector emitter voltage
difference and the collector current difference rf = ΔVce/
ΔIc while Vf0 is the value in the curve corresponding to
the actual collector current flow in the device.
Substituting the expression for the forward voltage in
Equation (2) into Equation (1) gives
2
Pc = V f I av + rf I rms
Conduction loss in mosfet is given by the equation.
Pc (Q1) = I 2 RMSQ1 * RDS ON
Where Iav and Irms are the average and the rms current
passing through the device in the conduction period.
These are calculated as follows:
1 T1
i0 (t )dw
T ∫0
1 T2
2
irms
= ∫ i02 (t )dw
T 0
iav =
5.2 Switching Losses
The switching losses are the total sum of on-state switching
losses and turn-off switching losses. They depend on the
device characteristics, switching frequency and device
current. The switching energy is expressed as a function
of the device current as:
Esw = k1i
Where k1 is got from the switching energy graph in
the device datasheet. The switching loss for the device is
calculated as:
Psw =
4
f s Ts
k1 i dwt
2p ∫0
Vol 8 (28) | October 2015 | www.indjst.org
6. Evaluation of Conversion
Losses in Two-Level
Converters
If the load current is assumed as Ia(wt) = ImSin (wt-0) then
the leg phase voltage is defined as Va(wt) = VmSin (wt-0)
and the duty cycle for the device switches is:
1
dT 1 = dT 4 = [1− M sin wt ]
2
1
dT 4 = dD1 = 1− dT 1 = [1− M sin wt ]
2
The average and rms currents for IGBTs T1 and T2 are
calculated using respective formulae and the duty cycle
defined as below:
 1
1 p+q
M cos q 
dT 1ia dw = I m  +

 2p
2p ∫q
8 
 1 M cos q 
1 p+q
IT 4,av =
dT 4iadw = I m  −

∫
q

2p
8 
 2p
 1 M cos q 
1 p+q
I 2T 1,rms =
dT 1iadw = I 2 m  +

2p ∫q
3p 
 8
 1 M cos q 
1 p +q
I 2T 4,rms =
dT 4 I 2adw = I 2 m  −

2p ∫q
3p 
 8
IT 1,av =
The average and rms currents for the lower freewheeling diode are similar to that of the upper IGBT
device but in opposite direction therefore:
 1
M cos q 
I D1,av = −IT 4,av = −I m  +

8 
 2p
 1
M cos q 
I D 4,av = −IT 1,av = −I m  +

8 
 2p
 1 M cos q 
I 2 D1,rms = −I 2T 4,rms = −I 2 m  +

3p 
 8
 1 M cos q 
I 2 D 4,rms = −I 2T 4,rms = −I 2 m  +

3p 
 8
The free-wheeling diode is switched on/off very fast
compared to the IGBT so its switching losses are relatively
small compared to that in an IGBT, therefore are not
considered in the calculation. The switching losses for the
IGBT are calculated using below equation as:
Psw =
k1 f s
2p
∫
0
p +q
I m sin(wt − q )dwt =
k1 f s I m
p
7. Comparisions
By substituting the values of the device parameters in
the loss evaluation formulae the respective values of the
losses have been tabulated in the below Tables 4,5,6,7 for
the respective switching frequencies of 5khz, 8khz, 10khz,
15khz.
Indian Journal of Science and Technology
Trinadh Mathe and K. Narsimha Raju
Table 6. Power loss comparison (FS = 5KHZ)
Table 9. Power loss comparison (FS = 15KHZ)
Conduction loss (per
leg)
Switching loss per
device
Total inverter loss
Conduction loss (per
leg)
Switching loss per
device
Total inverter loss
Si IGBT system
IGBT - 88.135w
Diode -57.986w
13.20w
Sic mosfet system
Mosfet- 59.91w
Diode - 57.986w
1.814w
517.563w
364.79w
Si IGBT system Sic mosfet system
IGBT - 88.135w Mosfet- 59.91w
Diode -57.986w Diode - 57.986w
39.6w
5.442w
675.963w
386.35w
Table 7. Power loss comparison (FS = 8KHZ)
Conduction loss (per
leg)
Switching loss per
device
Total inverter loss
Si IGBT system Sic mosfet system
IGBT - 88.135w Mosfet- 59.91w
Diode -57.986w Diode - 57.986w
21.12w
2.90w
565.08w
371.1w
Table 8. Power loss comparison (FS = 10KHZ)
Conduction loss (per
leg)
Switching loss per
device
Total inverter loss
Si IGBT system Sic mosfet system
IGBT - 88.135w
Mosfet- 59.91w
Diode -57.986w Diode - 57.986w
26.4w
3.62w
596.76w
375.42w
Figure 7. Loss comparison of simulated scenarios of
switching frequencies of 5khz, 10khz, 15khz for Si IGBT
versus sic mosfet.
The modelled si igbt based 2 level three phase spwm
inverter with modelled switches was simulated and
compared with sic mosfet based 2 level three phase spwm
Figure 5. Pspice simulated si IGBT based three phase spwm inverter (FS = 10KHZ).
Vol 8 (28) | October 2015 | www.indjst.org
Indian Journal of Science and Technology
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Comparitive Loss Evaluation of Si IGBT Versus Sic Mosfet (Silicon Carbide) for 3 Phase Spwm Inverter
Figure 6. Pspice simulated sic mosfet based three phase spwm inverter (FS = 10KHZ).
inverter using orcad pspice as simulation tool.
Figures 5 and 6 show the 2 scenarios one with si igbt
and sic mosfet at switching frequency of 10khz.
Power loss is compared in orcad pspice at various
switching frequencies and average power loss is measured
across each switch for 20ms and compared.
8. Conclusion
In sum, a 22kw sic mosfet base 3 phase spwm inverter
system is designed and compared with that of si igbt base
three phase spwm inverter at switching frequency ranges
of 5khz, 8khz, 10,khz, 15khz and it had been observed
that the losses of the 3 phase spwm sic mosfet inverter
where 29% less for 5khz switching frequency, 34% less
for switching frequency of 8khz, 37% less for switching
frequency of 10khz, 42% less for the switching frequency
of 15khz over the 3 phase spwm inverter based on si igbt
which in turn shows that the sic mosfet can be replaced
by si igbt in 3 phase spwm inverter system for better
efficiency and the pspice simulations showed similar
results showing that sic mosfet is efficient than si igbt
based three phase spwm inverter.
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